1. Field of the Invention
The present invention relates to a gas measuring device suitable for use with the processing apparatus in which a certain process of process gas is applied to objects to be processed, and also relates to a processing apparatus provided with the gas measuring device.
2. Description of the Related Art
Most semiconductor manufacturing apparatuses including the heat treating apparatus, diffusing apparatus, etching apparatus, sputtering apparatus and others are intended to process the surface of objects to be processed such as semiconductor wafers by process gases supplied. They are exhausted after this surface process and their certain processes are then finished.
In the case of the heat treating apparatus of the batch type, for example, SiH.sub.2 Cl.sub.2 gas is supplied as reaction gas into the reaction tube through the reactive gas supply pipe, Si film is formed on the surface of each of wafers positioned at the soaking zone in the reaction tube, and gas remaining in the reaction tube is then exhausted through the exhaust pipe by the vacuum pump connected to the exhaust pipe. The process is thus finished. After the finish of this process, purge gas such as inactive N.sub.2 gas is introduced into the reaction tube through the reactive gas supply pipe to replace atmosphere in the reaction tube by N.sub.2 gas. The semiconductor wafers which have been processed are then unloaded out of the reaction tube.
However, it has been found that the remaining reaction gas still discharged, though low in density, from the reaction gas supply pipe and adheres to the inner wall of the reaction tube and the surface of each of the processed objects, even when the reaction tube is purged by the purge gas such as N.sub.2 gas. This remaining reaction gas creates harmful substances and particularly in the case of SiH.sub.2 Cl.sub.2 gas it creates poisonous and corrodible HCl on the way of its reaction. It is therefore asked that HCl is measured even if its amount is extremely small. However, a device has not yet been provided to continuously measure such gas component that is low in density and extremely small in amount.